1. Field of the Invention
This invention relates to a process for the liquid phase separation of inositol and/or sorbitol from mixtures containing same. More particularly and in a preferred embodiment, this invention relates to such a separation by selective adsorption onto certain types of zeolitic molecular sieves.
2. Description of the Prior Art
Both inositol and sorbitol are sugar alcohols which have higher market value than do the common sugars. Inositol is a generic name for a family of cyclohexanehexols (hexahydroxycyclohexane C.sub.6 H.sub.6 (OH).sub.6, in which there are nine possible stereoisomers. Of these possible isomeric forms, one occurs in predominance in nature and is known by various names including meso -inositol, myo -inositol, i -inositol, inosite, dambose, meat sugar or muscle sugar. Myo -inositol is a commercially important compound and has certain physiological activities. It is a member of the Vitamin-B complex, in which role it possesses activity as a growth factor for certain animals and microorganisms. It also is a factor in the regulation of fat and cholesterol metabolism in higher animals. For convenience purposes only, myo -inositol will be hereinafter referred to simply as inositol. In addition, although the present invention has been shown to be useful for the separation of myo -inositol, it is expected that some other inositol isomers, other than myo -inositol, could also be separated by the same process. For a more complete description of inositol and its properties, see Kirk-Othmer Encyclopedia of Chemical Technology, 2d Ed., Vol. 11 (1966), pp. 673-676.
No commercial process for the synthetic production of inositol is known to the present inventors. However, because it widely exists in living cells, it is possible to extract inositol from plants. Inositol exists in the free form in many fruits; for example, about 8 weight % of the soluble carbohydrates in almond hulls is inositol and about 1.2 weight % of the fresh weight of the berries of Loranthacene is inositol. Inositol also exists as the hexaphosphate (i.e., phytic acid) in the seeds of many plants. For example, about 2 weight % of corn "steepwater" solids (a by-product of the wet milling of corn) is phytic acid and inositol is currently commercially produced by recovery from such corn steepwater. Specifically, the phytic acid, which has the following composition (as the acid) C.sub.6 H.sub.6 (OPO[OH].sub.2).sub.6, is first precipitated out as a calcium/magnesium salt. The salt is hydrolyzed to inorganic phosphate and inositol, the inorganic phosphate is removed by precipitation and the inositol recovered by repeated crystallization. This process is both expensive and onerous, involving digestion at 100.degree.-200.degree. C. in strong acids or bases, etc.
Sorbitol may be made by the reduction of sugars and is an important commercial polyhydric alcohol in its pure form. Sorbitol has many uses, for example as a humectant in cosmetics or it may be used to make polyethers which are useful in plastics.
Commonly-assigned copending U.S. patent application Ser. No. 329,608, filed Dec. 10, 1981, now abandoned, discloses a process for the liquid phase separation of sorbitol and mannitol by selective adsorption on certain types of zeolite molecular sieves. Specifically, Table II at page 7 thereof, discloses selectivity for sorbitol by several cation forms of type X and type Y zeolites.